Fay Horak recently published a report suggesting there may be more balance problems with STN as compared to GPi DBS. Fay is at the NPF Center of Excellence in Oregon.

Below is the abstract from her recent paper:

J Neurosurg. 2012 Mar 16. [Epub ahead of print]
The effects of subthalamic and pallidal deep brain stimulation on postural responses in patients with Parkinson disease.
St George RJ, Carlson-Kuhta P, Burchiel KJ, Hogarth P, Frank N, Horak FB.
Source
Departments of Neurology and.
Abstract
Object The effect of deep brain stimulation (DBS) for Parkinson disease (PD) on balance is unclear. The goal of this study was to investigate how automatic postural responses (APRs) were affected in patients randomized to either subthalamic nucleus (STN) or globus pallidus internus (GPi) surgery. Methods The authors tested 24 patients with PD who underwent bilateral DBS, 9 control patients with PD who did not undergo DBS, and 17 age-matched control volunteers. The electrode placement site was randomized and blinded to the patients and to the experimenters. Kinematic, kinetic, and electromyographic recordings of postural responses to backward disequilibrium via forward translations of the standing surface were recorded in the week prior to surgery while the patients were off (OFF) and on (ON) antiparkinsonian medication (levodopa), and then 6 months after surgery in 4 conditions: 1) off medication with DBS switched off (OFF/OFF); 2) off medication with DBS on (DBS); 3) on medication with DBS off (DOPA); and 4) with both medication and DBS on (DBS+DOPA). Stability of the automatic postural response (APR) was measured as the difference between the displacement of the center of pressure and the projected location of the center of body mass. Results Patients with PD had worse APR stability than controls. Turning the DBS on at either site improved APR stability compared with the postoperative OFF condition by lengthening the tibialis response, whereas medication did not show an appreciable effect. The STN group had worse APR stability in their best functional state (DBS+DOPA) 6 months after the DBS procedure compared with their best functional state (ON levodopa) before the DBS procedure. In contrast, the GPi group and the PD control group showed no change over 6 months. The APR stability impairment in the STN group was associated with smaller tibialis response amplitudes, but there was no change in response latency or coactivation with gastrocnemius. Conclusions Turning the DBS current on improved APR stability for both STN and GPi sites. However, there was a detrimental DBS procedural effect for the STN group, and this effect was greater than the benefit of the stimulating current, making overall APR stability functionally worse after surgery for the STN group.

In order to better understand what this topic and the referenced article are trying to tell a prospective PD DBS candidate, may I ask about the logic of your post: the deductions and implications
... which is often necessary when one sees the same issue addressed differently by various expert sources:
- the NPF is designating OHSU in Portland OR as a "center of excellence" ... whatever that means at one time or another for the quality of service ... and whether such a center still has the funding needed for a high level patient support corresponding to clinical studies of GPi vs. STN
- OHSU has published for years on its preference of the GPi target over the STN target for PD DBS
Does this ad up to your group making a favorable recommendation for the GPi target over the STN target for PD gait and balance symptoms?

For a more complete picture of how this fits into gait and balance therapy of PD, how about the "rest of the story"?
- while a number of other neuro-surgical teams are still willing to address the STN vs. GPi story impartially ... twice as many conference papers seem to favor the STN over GPi for this symptom
- or better said, this is one of the axial symptoms which don't respond well to DBS in either target; hence an interest in the PPN target
- how about addressing the high number of patient stories of gait and postural stability having deteriorated post-DBS; whether these situations are related to particular choices of stimulation parameters (e.g. frequency ) or PD progression stage

Putting all this together, a DBS candidate (having been already evaluated by the team) may wish to ask the following question (as a way to evaluate the team and the outcomes of the procedure):
- if his / her critical movement disorders are predominantly axial, i.e communication (dysarthria) and locomotion (falling), and don't respond to levodopa, can any DBS targeting strategy specifically address those symptoms?
- or if no such symptoms exist pre-op, what are the cances that they may appear soon post-DBS, as side effects of stimulating certain neural bundles? and not get resolved within say one year's therapy.

The most important issue is that PD progresses and axial symptoms such as gait, balance and speech/swallow may progress despite STN or GPi DBS.

Though the Portland study is small it is interesting to hypothesize that there may be different neural bundles stimulated with STN vs. GPi DBS and that there may be specific symptoms that do slightly better with a different target.

I think it will be great if we can keep studying the comparison so that patients facing the choice pre-operatively will have all the information.